Various types of riser tensioners have been devised for use in the oil and gas industry. These tensioners help to maintain a desired tension on a riser extending between a subsea oil well and a surface (e.g., floating) platform. Ram-style riser tensioners are often used to provide tension to risers used in spar and tension leg platform (TLP) applications. Ram-style riser tensioners may also be used in dry tree semi-submersible applications. Ram-style tensioners include hydro-pneumatic cylinders used to maintain a nearly constant tension on production risers or drilling risers as the floating platform moves in the ocean due to waves, current, and other factors.
In conventional ram-style tensioners, the cylinders are exposed to a variety of different loading conditions. Unfortunately, traditional ram-style tensioners can have difficulty resisting bending loads that may be imparted to the hydro-pneumatic cylinders of the tensioners. For example, tensioner systems are typically designed so that if one cylinder fails, the remaining cylinders are able to maintain a desired tension in the riser. However, during this scenario, large bending moments can be applied to the riser due to the imbalance in the tension load being supported by the remaining cylinders. In addition, the cylinders can be exposed to compression due to movements occurring on the platform. In some instances, the ram-style tensioners can be exposed to torsion, where the direction of the cylinder force tends to add to the torsional loading rather than resisting it.
To address these different loading conditions and to protect the riser from bending, existing tensioners often include complex structures for guiding the riser while reducing the bending force on the cylinders. Unfortunately, these structures can be bulky and may reduce operator access to surface wellhead and tree equipment.